The expression "mesoporous" as used throughout this specification refers to pores having diameters in the range of from 1.5 to 20.0 nm.
Crystalline mesoporous molecular sieves are known in the art. For instance, in International patent specification No. WO 93/02013 a mesoporous molecular sieve is disclosed, which, after calcination, exhibits an X-ray diffraction pattern with the strongest peak (i.e. relative intensity is 100) at a d-spacing d.sub.1 of at least 1.8 nm and at least one additional weaker peak (relative intensity up to 49) at a d-spacing d.sub.2 such that the ratio d.sub.2 /d.sub.1 has a value of 0.87 0.06. The molecular sieve is suitably prepared by adding a silicon oxide source and optionally an aluminum oxide source to a solution containing an organic templating agent, followed by agitating the mixture thus obtained for 10 minutes to 6 hours at a temperature of from 0 to 50.degree. C. and a pH of 7 to 14 and finally crystallizing the agitated mixture at a temperature of 50 to 200.degree. C., preferably 95 to 150.degree. C., for 4 to 72 hours. The crystallized material recovered is then calcined to eventually arrive at the crystalline mesoporous molecular sieve envisaged.
In International patent specification No. WO 93/01884 a catalyst composition is disclosed of which the support component comprises a non-layered mesoporous molecular sieve which, in calcined form, exhibits an X-ray diffraction pattern with at least one peak having a relative intensity of 100 at a d-spacing of at least 1.8 nm and which has a benzene sorption capacity greater than 15 grams benzene per 100 grams of the material at 6.7 kPa and 25.degree. C. Several methods are disclosed for preparing the mesoporous material, but all methods typically involve preparing a starting mixture containing the necessary components including an organic templating agent and sources of oxides of silicon and optionally aluminum, followed by crystallization of the material at a pH of at least 9 and at a temperature which suitably is above 50.degree. C., but which--as becomes apparent from the working examples--in practice ranges from 95 to 150.degree. C. Crystallization time ranges from 4 hours (at 105.degree. C.) in example 19 to 192 hours plus an additional period of about 12 hours (at 95.degree. C.) in example 3. In most working examples, however, crystallization temperatures of about 100.degree. C. for periods of time of 20 to 90 hours are applied.
In International patent specification No. WO 95/30625 a process for preparing mesoporous molecular sieves similar to those described in WO 93/01884 is disclosed, wherein the molecular sieve is crystallized at a pH from 3 to 8 from a starting mixture containing a specified amount of fluoride in addition to the required oxide sources and organic templating agent(s). Crystallization conditions typically involve temperatures of from 60 to 250.degree. C., preferably from 90 to 200.degree. C., for a period of time of from 2 to 336 hours, but most suitably from 24 to 120 hours.
Although the prior art processes for preparing mesoporous molecular sieves perform satisfactory, there is still room for improvement, particularly in terms of crystallization temperature and crystallization time. It will be appreciated that lower crystallization temperatures and shorter crystallization times are attractive from an economic perspective. Lower temperatures, namely, require less expensive equipment, whilst shorter crystallization times make higher product yields per unit of time possible. In addition, the high temperature resistance and crystallinity of the prior art mesoporous materials are, though acceptable, not yet at an optimum level. Particularly when applied as support material in catalysts, mesoporous molecular sieves being stable at temperatures up to 100.degree. C. and having increased crystallinity are desired.